Late Eocene–Pliocene basin evolution in the Eastern Cordillera of northwestern Argentina (25°–26°S): regional implications for Andean orogenic wedge development

Important aspects of the Andean foreland basin in Argentina remain poorly constrained, such as the effect of deformation on deposition, in which foreland basin depozones Cenozoic sedimentary units were deposited, how sediment sources and drainages evolved in response to tectonics, and the thickness of sediment accumulation. Zircon U‐Pb geochronological data from Eocene–Pliocene sedimentary strata in the Eastern Cordillera of northwestern Argentina (Pucará–Angastaco and La Viña areas) provide an Eocene (ca. 38 Ma) maximum depositional age for the Quebrada de los Colorados Formation. Sedimentological and provenance data reveal a basin history that is best explained within the context of an evolving foreland basin system affected by inherited palaeotopography. The Quebrada de los Colorados Formation represents deposition in the distal to proximal foredeep depozone. Development of an angular unconformity at ca. 14 Ma and the coarse‐grained, proximal character of the overlying Angastaco Formation (lower to upper Miocene) suggest deposition in a wedge‐top depozone. Axial drainage during deposition of the Palo Pintado Formation (upper Miocene) suggests a fluvial‐lacustrine intramontane setting. By ca. 4 Ma, during deposition of the San Felipe Formation, the Angastaco area had become structurally isolated by the uplift of the Sierra de los Colorados Range to the east. Overall, the Eastern Cordillera sedimentary record is consistent with a continuous foreland basin system that migrated through the region from late Eocene through middle Miocene time. By middle Miocene time, the region lay within the topographically complex wedge‐top depozone, influenced by thick‐skinned deformation and re‐activation of Cretaceous rift structures. The association of the Eocene Quebrada del los Colorados Formation with a foredeep depozone implies that more distal foreland deposits should be represented by pre‐Eocene strata (Santa Barbara Subgroup) within the region.     

Uncertainty in Carbon Capture and Storage (CCS) deployment projections: a cross-model comparison exercise

Carbon Capture and Storage (CCS) can be a valuable CO₂ mitigation option, but what role CCS will play in the future is uncertain. In this paper we analyze the results of different integrated assessment models (IAMs) taking part in the 27th round of the Energy Modeling Forum (EMF) with respect to the role of CCS in long term mitigation scenarios. Specifically we look into the use of CCS as a function of time, mitigation targets, availability of renewables and its use with different fuels. Furthermore, we explore the possibility to relate model results to general and CCS specific model assumptions. The results show a wide range of cumulative capture in the 2010–2100 period (600–3050 GtCO₂), but the fact that no model projects less than 600 GtCO₂ indicates that CCS is considered to be important by all these models. Interestingly, CCS storage rates are often projected to be still increasing in the second half of this century. Depending on the scenario, at least six out of eight, up to all models show higher storage rates in 2100 than in 2050. CCS shares in cumulative primary energy use are in most models increasing with the stringency of the target or under conservative availability of renewables. The strong variations of CCS deployment projection rates could not be related to the reported differences in the assumptions of the models by means of a cross-model comparison in this sample.     

Distribution, abundance, and habitat characteristics of juvenile tautog (Tautoga onitis, family labridae) in Narragansett Bay, Rhode Island, 1988–1992

Estuarine nursery areas are critical for successful recruitment of tautog (Tautoga onitis), yet they have not been studied over most of this species' range. Distribution, abundance and habitat characteristics of young-of-the-year (YOY, age 0) and age 1+juvenile tautog were evaluated during 1988–1992 in the Narragansett Bay estuary, Rhode Island, using a 16-station, beach-seine survey. Estuary-wide abundance was similar among years. Greatest numbers of juveniles were collected at northern Narragansett Bay stations between July and September. Juvenile abundances varied with density of macroalgal and eelgrass cover; abundances ranged from 0.03 fish per 100 m² to 8.1 fish per 100 m². Although juveniles use eelgrass, macroalgae is the dominant vegetative cover in Narragansett Bay. Macroalgal habitats play a previously unrealized, important role and contribute to successful recruitment of juvenile tautog in Narragansett Bay. Juvenile abundances did not vary with sediment type or salinity, but were correlated with surface water temperature. Fish collected in June were age 1+ juveniles from the previous year-class (50–167 mm TL) and these declined in number after July or August. The appearance of YOY (25–30 mm TL) in July and August was coincident with the period of their greatest abundances. A precipitous decline in abundance occurred by October because of the individual or combined effects of mortality and movement to alternative habitats. Based on juvenile abundance, a previously unidentified spawning area was noted in Mount Hope Bay, a smaller embayment attached to the northeastern portion of Narragansett Bay. In August 1991, Hurricane Bob disrupted juvenile sise distribution and abundance, resulting in reduced numbers of YOY collected after the storm and few 1+ juveniles in 1992.     

Interpreting the hydrological history of a temporary pond from chemical and microscopic characterization of siliceous microfossils

The hydrological history of a temporary pond in South Carolina was inferred from a 5500-year record of siliceous microfossils, including diatoms, freshwater sponge spicules, chrysophyte cysts, plates of testate amoebae and plant phytoliths. Microfossil abundance was estimated by microscopic quantification of siliceous particles and by chemical extractions of silica. Diatom, sponge and mineral particle volumes were correlated with silica concentrations attributable to these fractions. Both techniques suggested a sequence of four distinct community types. Basal sediments (4630–5520 ¹⁴C YBP) containing phytoliths and sponge spicules indicative of a wetland community were covered by sediments dominated by the remains of planktonic protists (3750–4630 ¹⁴C YBP) suggesting a transition from a vegetated marsh to an open-water, permanently flooded pond. Microfossil assemblages above this zone indicate the return of a wetland community ca. 3750 YBP that persisted until recently, when pond water levels stabilized as a result of seepage from a reservoir constructed nearby in 1985. This study suggests that the suite of siliceous microfossils commonly found in pond sediments can be used to infer historical alternations between macrophyte and plankton-dominated states in shallow basins. Regional climate inferences from this record include a mid-Holocene hydrological maximum and the onset of the modern climate ca. 3500 YBP.     

The dynamics of central Main Ethiopian Rift waters: Evidence from δD, δO and Sr/Sr ratios

Water samples from cold and geothermal boreholes, hot springs, lakes and rivers were analyzed for δD, δ¹⁸O and ⁸⁷Sr/⁸⁶Sr compositions in order to investigate lake water–groundwater mixing processes, water–rock interactions, and to evaluate groundwater flow paths in the central Main Ethiopian Rift (MER) of the Ziway–Shala basin. Different ranges of isotopic values were recorded for different water types: hot springs show δ¹⁸O −3.36 to +3.69 and δD −15.85 to +24.23, deep Aluto-Langano geothermal wells show δ¹⁸O −4.65 to −1.24 and δD −12.39 to −9.31, groundwater wells show δ¹⁸O −3.99 to +5.14 and δD −19.69 to +32.27, whereas the lakes show δ¹⁸O and δD in the range +3.98 to +7.92 and +26.19 to +45.71, respectively. The intersection of the Local Meteoric Water Line (LMWL: δD = 7 δ¹⁸O + 11.2, R² = 0.94, n = 42) and the Local Evaporation Line (LEL: δD = 5.63δ¹⁸O + 8, n = 14, R² = 0.82) was used to estimate the average isotopic composition of recharge water into the basin (δD = −5.15 and δ¹⁸O = −2.34). These values are depleted if compared with the modern-day average precipitation, presumably indicating paleo-groundwater components recharged during previous humid climatic phases. The measured stable isotope values indicate that the geothermal wells, some of the hot springs and groundwater wells mainly consist of meteoric water. The Sr isotopic signatures in all waters are within the range of the Sr isotopic composition of the rift basalts and rhyolites. The variability of Sr isotopic data also pinpoints complex water–rock interaction and mixing processes in groundwater and surface water. The ⁸⁷Sr/⁸⁶Sr ratio ranges from 0.70445 to 0.70756 in the hot springs, from 0.70426 to 0.70537 in two deep geothermal wells, and from 0.70673 to 0.70721 in the rift lakes Ziway, Langano, Shala and Awasa. The radiogenic composition recorded by the lakes indicates that the input water was predominantly affected by progressive interaction with rhyolitic volcanics and lacustrine sediments.     

Carolina Bay geoarchaeology and Holocene landscape evolution on the Upper Coastal Plain of South Carolina

Surface water on the mainly dry, upland interfluves of the Upper Coastal Plain of South Carolina occurs currently as a sporadic distribution of shallow ponds held within Carolina bays and other small, isolated basins. At seven bays on the U.S. Department of Energy's Savannah River Site on the Upper Coastal Plain of South Carolina, we investigated Holocene changes in bay morphology, ecology, and prehistoric human activity. At Flamingo Bay, we employed archaeological survey and testing, shovel and auger testing, sediment analysis, and ground-penetrating radar to document stratigraphy and chronology of the sand rim on the eastern side of the bay. Artifact assemblage indicate changes in intensity of human use of the bay. Radiocarbon dates from a sediment core establish time scales for depositional processes at the center of the basin. Ground-penetrating radar data from the other bays indicate that the stratigraphy of all seven bays is broadly similar. We conclude that: (1) Significant modification of the bays, including rim development and basin infilling, occurred during the Holocene; (2) ponds on the early Holocene landscape were larger and more permanent than at present; (3) early Holocene climate, as indicated by both depositional processes and human activity, was not characterized by prolonged periods of extremely dry conditions; and (4) fluvial-centric models of terminal Pleistocene—early Holocene human adaptations require revision to include intensive use of isolated upland ponds. © 1996 John Wiley & Sons, Inc.